Many pathophysiological processes in the cardiovascular system such as thrombosis, vessel wall injury, and atherosclerosis occur in the presence of fluid shear forces. These shear forces have a direct mechanical effect on the vessel wall and can also indirectly affect wall properties by mediating the interactions of blood elements with the lumenal surface. The normal integrity of vessel wall is maintained by a delicate monolayer of endothelial cells on this lumenal surface. The aim of this project is to investigate the interactions of fluid shear forces with the vessel wall surface by utilizing endothelial cells grown in monolayer culture in a specially designed flow chamber. Morphological, cytoskeletal, and metabolic changes in the endothelial cells are being investigated as a function of fluid shear stresses on the cell surface. The flow chamber consists of a parallel plate geometry which accomodates Thermanox circular cover slips upon which human umbilical cord endothelial cells are cultured. The flow patterns and shear stress values within the chamber have been characterized using electrochemical shear measurements, flow visualization techniques, and laser doppler anemometry during steady flow. We have tested the chamber at shear stresses up to 20 dynes square centimeter. The flow remains laminar in the test region over the cover slips. Laser Doppler velocity profiles have characteristic parabolic shape. Both the velocity profiles and the measured shear agree to within 10% of theoretical values for parallel plate flow. With no flow, the cells form a random pattern of cobblestone cells with no orientation. Little or no orientation is observed at shear stresses from 4 to 7 dynes square centimeter up to 72 hours. At 8 to 12 dynes square centimeter, cell orientation is observed by 48 to 72 hours. At shear stresses from 12 to 16 dynes square centimeter, the cells have oriented within 24 hours. A radio-immunoassay is being developed to measure the production of von Willibrand factor and Factor VIII during shear experiments.